Quantum device manipulates and measures four spin states of a single nucleus.

Spin is one of the intrinsic quantum properties of particles. The spin of electrons orbiting an atom has significant consequences, such as determining the magnetic properties of materials. Atomic nuclei also have spin, but that is harder to manipulate: it interacts less with other spins and nuclei are much more massive, so they aren't as easily moved. However, those very properties could make nuclear spin a good option for for quantum computing, since the spin state of a nucleus is less subject to environmental influences that might alter its state. But reading out the nuclear spin state is notoriously difficult.

A new proof-of-principle experiment by Romain Vincent, Svetlana Klyatskaya, Mario Ruben, Wolfgang Werndorfer, and Franck Balestro measured the nuclear spin of a single atom. The nucleus belonged to a terbium (Tb) ion inside a larger molecule, which the researchers linked to a gold nanowire to construct a transistor-like device. They measured the four possible nuclear spin states, and observed them to be stable for tens of seconds—long enough to perform entanglement and other quantum-information processes.

Spin is integral to particles: all electrons (for example) have the same amount of spin. The spin quantum state is the relative orientation of the spin with respect to some other spin, or to an external magnetic field. Electrons are low mass particles and relatively lightly bound to atoms, so their spins are fairly easy to manipulate. As a result, the spins of atoms are typically determined by their electrons—including the magnetic properties. However, because electrons' spins are subject to strong environmental influences, they are somewhat unreliable from a quantum information perspective. If you write information to an electron's spin, it won't stay written for long.

Atomic nuclear spin is less strongly linked to the environment, which makes it both harder to manipulate and to measure. However, if those problems can be overcome, nuclear spin could potentially be better for quantum computing, since it's relatively stable.

The technique described in a recent Nature paper involves creating a single-molecule magnet (SMM). While they are not "permanent magnets" (ferromagnets), which possess magnetic properties in isolation, SMMs exhibit significant magnetism when exposed to an external magnetic field. In this case, the SMM was a triply ionized terbium atom (Tb3+) sandwiched between two complex organic molecules (called aromatic phthalocyanine (Pc) ligands, for the curious). The missing electrons in the Tb3+ and its coupling to the organic molecules made the nuclear spin far more accessible to external stimuli. The particular spin configuration had four possible quantum states (making it a spin-3/2 system, in contrast to the two-state, spin-1/2 electrons).

The SMM was deposited on a gold nanowire with three connection points, so that it acted as a transistor. While under ordinary (equilibrium) conditions, all four spin states would be equally probable, the researchers could induce transitions between them by adjusting the voltage at the connection points. The particular transition used a phenomenon known as quantum tunneling of magnetization (QTM)—the Tb normally wouldn't be able to switch magnetic states, but by applying that external current, these transitions could occur.

They also were able to measure how the quantum state of the Tb3+ changed over time, showing that the induced spin state was stable over a period of several seconds, after which thermal and other fluctuations damped out the particular chosen spin state until all four states occurred with equal likelihood. While this is a short period in everyday terms, it's quite stable by quantum standards.

Stable, coherent spin states that can be measured non-destructively are extremely useful for quantum computing. Two or more such states could be entangled, allowing for the implementation of algorithms and transfer of information. The terbium ion also possesses four quantum states, meaning the SMM transistor could potentially realize algorithms that currently only lie in the realm of theory. While this experiment only involved one SMM at a time and therefore didn't implement entangled states, it's a significant step toward studying quantum devices based on nuclear spin.

I'm sure a cadre of IP lawyers are convening right now to make sure that any applications of this technology are tied up in lawsuits for years, lest someone accidentally use it to improve anybody's cellphone experience.

Not a problem, I plan on using my phone on Pluto. (Does ATT have service on Pluto?)

Does AT&T have service anywhere? Having just driven San Fran --> [around the entire bay] --> Reno --> Salt Lake City --> Yellowstone --> Canadian border I can reasonably reliably say that across six separate states the answer is "in Salt Lake City, sort of, if you stand in the right place. And Pray."

$deity I was glad to see the Canadian border. As soon as I was within visual distance, HSPA started working again, and hasn't stopped since.

Going back a number of years (4? 5? 6?) Wollongong University here in Australia did something similar. In short, they could control the rotation direction of the electrons of an atom.

Story at the time was that this could be used as a binary on/off state, meaning every atom in an object could, in theory, be a bit for a data storage device. Because of the nature of atoms, once the spin direction was set, it didnt change, or something like that, so was a very permanent storage that couldnt just be wiped with a magnet.

And anything could be the storage.

Imagine an iPod where the casing stored all the music, or a camera which housed the pictures within the battery.

Good to see the technology develop, and others expanding on it. Might be 20 or even 50 years before we see real world usage for this, but its promising. Imagine the Library of Congress stored in the head of a pin...

Transport measurements were taken using a lock-in amplifier in a dilution refrigerator with an electronic temperature of about 0.08 K

You can get your cellphone as long as you don't mind toting around several hundred pounds, and a few hundred thousand dollars, worth of cryostat.

Not a problem, I plan on using my phone on Pluto. (Does ATT have service on Pluto?)

Thanks to this wonderful and theoretical universe, you will have service! All thanks to ATT's Share Anything plan, which quantum entangles any of your phones to the network. Now for only $69.99 a month!

Transport measurements were taken using a lock-in amplifier in a dilution refrigerator with an electronic temperature of about 0.08 K

You can get your cellphone as long as you don't mind toting around several hundred pounds, and a few hundred thousand dollars, worth of cryostat.

Not a problem, I plan on using my phone on Pluto. (Does ATT have service on Pluto?)

Thanks to this wonderful and theoretical universe, you will have service! All thanks to ATT's Share Anything plan, which quantum entangles any of your phones to the network. Now for only $69.99 a month!

The technique described in a recent Nature paper involves creating a single-molecule magnet (SMM). While they are not "permanent magnets" (ferromagnets), which possess magnetic properties in isolation, SMMs exhibit significant magnetism when exposed to an external magnetic field. In this case, the SMM was a triply ionized terbium atom (Tb3+) sandwiched between two complex organic molecules (called aromatic phthalocyanine (Pc) ligands, for the curious). The missing electrons in the Tb3+ and its coupling to the organic molecules made the nuclear spin far more accessible to external stimuli. The particular spin configuration had four possible quantum states (making it a spin-3/2 system, in contrast to the two-state, spin-1/2 electrons).

Just a few technical points. Any paramagnet (SMM or not) exhibits significant magnetization when exposed to an external magnetic field. The distinguishing characteristic of a ferromagnet is that the magnetic dipoles are all aligned in one direction, even in the absence of a magnetic field (this is a result of the favorable coupling between parallel-aligned spins) whereas paramagnets relax and their magnetic moments are randomized after removal of the magnetic field. Single-molecule magnets do in fact act, roughly, like "permanent" magnets. That's the whole point. (Granted they exhibit this behavior at a few Kelvin. If held at a temperature below the blocking temperature, they will retain their magnetization for months.)

sorry, ignorant non-physicist here - is electron spin related to each individual electron's rotation or is it the direction in which it rotates around the atom? or... both?

Electrons are point(ish) particles, so they don't actually spin. Macroscopic, electrically charged objects that spin produce magnetic fields; likewise, electrons are electrically charged objects that have intrinsic magnetic moments, and by loose analogy this magnetic moment is the result of the electron's "spin". As was said earlier, though, spin is an intrinsic property of an elementary particle and is not the result of any actual spinning.

There is another type of angular momentum of electrons in atoms (other than spin), known as orbital angular momentum. This is a more of classical phenomenon because it is roughly due the revolution of a charged particle (electron) about a point (the nucleus). But once again this is not a great analogy, as electrons don't actual orbit the nucleus in circular or elliptical paths, their positions, velocities, and energies around the nucleus are dictated by the Schrodinger equation, which is a quantum mechanical description of "where" electrons are about the nucleus. Anyway, this orbital angular momentum gives rise to an orbital magnetic moment. The interplay of the orbital magnetic moment and the spin magnetic moment of electrons is what, broadly speaking, gives rise to magnetic anisotropy and thus single molecule magnetism.

wonderful thanks. so electrons are "everywhere" in their orbit until measured (cat is alive/dead in the box until opened thing?) and their spin is both up and down until similarly determined? (thank you wiki.) the magnetism stuff bends my head but thanks again.